Apparatus for diathermic treatment



Jan. 18, 1938. F. D. WEBSTER APPARATUS FOR DIATHERMI'C TREATMENT Filed April 13, i955 @w% 6 Z Z c a Wm 3 Z. a 3 w 4 W 5o 2 fi a. w 7 0 HU 3M W 5. M 711 m vw a u M Fl; 5 C V w w w W a 2 a W 3 2 BLOWER INVENTOR:

FULLERTON D. h [BSTER Patented Jan. 18, 1938 UNl'i" grease PATENT OFFEQE AERARATUS FOR DIATHERMIC TREATMENT Application April 13, 1935, Serial N 16,133

10 Claims.

This invention relates to new and useful improvements in apparatus for diathermic treatment.

The object of the present invention is to provide a generator of very high frequency oscillations (oscillations substantially below a wave length of ten meters) which is simple to construct and operate, the output of which may be tuned to insure great efficiency and measured without waste of energy and which, therefore, is particularly adapted for use in apparatus for diathermic treatment.

The nature of the invention will more clearly appear from the following detailed description of a preferred embodiment diagrammatically illustrated in the drawing.

All of the power required is obtained from the electric light mains by means of. a flexible cord l to one end of which a plug is attached which may be inserted into a suitable outlet fixture. Since the usual voltage and frequency of electric light mains is 105 to 115 volts and 50 to cycles per second, respectively, the power supply equipment is designed accordingly. The other end of the cord is connected to terminal strip 2, which provides a convenient arrangement for distributing the power supply. However, before distribution the power supply is made to flow through a double pole single throw switch 3 which is properly fused in each blade. Power is then supplied to the primary winding 6 of a filament transformer 5, one side of the circuit being taken from one side of the switch 3 through adjustable rheostat 4 to one side of the Winding 6, the other side being taken first to the terminal strip 2 where it may be connected to the terminal which in turn connects to the other terminal of winding 5 or to another terminal connecting to a point intermediate the ends of winding 6. This alternate connection to include all or only part of the winding 6 is provided to take care of, differences in the voltage of the supply mains, the whole of winding 6 being used when the voltage is near 115 volts and part of the winding when the voltage is near volts. The secondary winding l of the transformer 5 is designed with respect to the number of turns relative to winding 6 to deliver a voltage suitable for filaments 8 and 9 of vacuum tubes l7 and 18, respectively. The ratio of the turns in winding 6 to those in Winding 7 is in the neighborhood of ten to one. The terminals of winding i are connected to terminals of the terminal strip 2 which in turn connect through choke coils ill and H to the filaments 8 and 9. A voltmeter l4, shunted by a capacitance I5, is connected across the filaments 8 and 9 in parallel, with a high frequency choke coil in series with each wire leading to the voltmeter. These high frequency choke coils I2 and I3 are designed to present a high impedance to the fiow of alternating current, the frequency of which is within the range generated by the vacuum tubes I7 and 18. Consequently, they suppress the flow of ultra-high frequency current in the voltmeter circuit. In order further to insure that ultra-high frequency currents cannot flow through the voltmeter i l, the capacitance l5 provides a low impedance by-pass without interfering with the proper functioning of the voltmeter. The voltmeter it provides a means of determining when the filament voltage has been adjusted to the proper value by the rheostat 4.

Power is supplied to a blower it through a pair of terminals on terminal strip 2 which pair of terminals is connected to the blades of the main power switch 3. The blower I6 is installed inside the cabinet housing the equipment in order to provide the needed cooling of the equipment.

The remainder of the power at the proper voltages is supplied to grids 2| and 22 and plates I9 and 28 of the vacuum tubes H and I8, respectively, through the agency of plate transformer 23. The voltage of the mains is connected through the proper terminals on the terminal strip 2 to the whole or part of the primary winding 23 in the same manner and for the same reason as explained in the case of primary winding 6 of the filament transformer 5. The secondary winding of transformer 23 comprises two parts 25 and 26 which constitute in effect a single winding tapped at a point intermediate the ends. This intermediate point is connected to ground thus providing a conductive connection to the filament circuit via a ground connected to one side of the filament choke coil II. This conductive connection with the filament circuit makes the voltages applied to the grids and plates of the vacuum tubes by the windings 25 and 26, respectively, bear a definite relation to the potential of the filament circuit. The free terminal of winding 25 is conductively connected to the grids 2| and 22 through a divided circuit comprising ultra-high frequency choke coil 28, one terminal of which is connected to the free terminal of. coil 25 and the other terminal of which is connected to the mid-point of inductance coil 29, which, in turn, has one terminal connected to the grid 2| and the other to the grid 22. Thus the voltage with respect to the filament circuit, which exists at the free terminal of coil 25, is

effectively applied to the grids 2i and 22 simultaneously. The choke 28 is designed to suppress the flow of ultra-high frequency current in the common lead. Capacitance 2'! shunted across the winding 25 serves to prevent oscillation of the tubes at some undesired. audio frequency, which might take place under the control of the windings of the plate power transformer. The free end of winding 26 is likewise conductively connected to the plates l9 and 20 through a divided circuit comprising ultra-high frequency choke coil 30, one terminal of which is connected to the free end of winding 26 and the other terminal of. which is connected to the mid-point of inductance coil 3! which, in turn, has one terminal connected to the plate l9 and the other to plate 29. Therefore, the voltage with respect to the filament circuit which exists at the free terminal of winding 26 is effectively applied to the plates 59 and 20 simultaneously. The ultra-high frequency choke coil 30 serves to suppress the ultra-high frequency current from flowing in the common lead.

Since the voltage of the main supply connected to the primary winding 24 is alternating at the rate of 50 to 60 cycles per second, the voltage induced in the secondary comprising windings 25 and 26 is likewise alternating at the same rate. It is evident that the voltage existing at any given instant, except when the instantaneous induced voltage is zero, at the free terminal of winding 26 is opposite in polarity to that existing at the free terminal of winding 25 at the same instant and, further, since the filament circuit is connected to an intermediate point, the potential applied to the grids 2| and 22 is negative with respect to the filament whenever the potential applied to the plates is positive with respect to the filament and vice versa. Whenever the potential applied to the plates is negative no plate current flows in the vacuum tubes l1 and i8 and the tubes are rendered for the moment inoperative. This situation arises during one half of each cycle of the supply voltage. During the other half of each cycle, the plates are made positive and the grids negative with respect to the filament circuit in which condition the tubes are operative. The number of turns in windings 25 and 26 are related to the number of turns in the primary winding 24 so that suitable voltages are applied to the grids and plates depending upon the design of the vacuum tubes l1 and The plate inductance coil 3| is not coupled to the grid inductance coil 29 but oscillations are maintained by virtue of the electro-static voltages induced on the grid from the plate of each tube through the grid plate capacity of the tube. Since the opposite terminals of coil 29 are connected tothe grids 2i and 22, and the grid biasing voltage to the mid-point of the coil 29, the induced voltages are super-imposed on the biasing voltage in such a manner that when the instan taneous voltage is reduced on grid 2! it is simutaneously increased by an equal amount on grid 22. The net effect is to cause corresponding alternations in the plate current of both tubes which flowing through coil 3| again induce an alternating voltage in coil 29, and so on. If the efiects of the induced grid voltages are correctly phased with respect to the plate current alternations, the circuit becomes self-sustaining, i. e., an oscillation generator. The conditions for selfoscillation are fulfilled substantially at the frequency for which the series circuit comprising 2 ll9--3l20-2229-2l is resonant. It is well known that the series resonant frequency of an electrical circuit depends upon the inductance and capacitance comprised in the circuit. The inductance of the oscillation circuit comprises coils 29 and iii and the capacitance comprises the inter-electrode capacitances between grid 2! and plate 59 of tube ll and between grid 22 and plate 25 of tube l8. It is apparent that ultra-high frequency alternating current may be generated since the interelectrode capacitances are extremely small and the coils 2e and 3! may be extremely small inductances. It is to be noted also that the divided circuit method of applying the grid and plate biasing potentials makes it possible to confine the ultra-high frequency oscillations to the circuit 2 ll 9-3 l-2ii22 292l and an output circuit about to be described.

vCoil 3! is inductively coupled to two coils 32 and 33 which form part of a tuned output circuit the additional parts of which are an uncoupled inductance 34 shunted by a measuring circuit and and an adjustable capacitance 35. Through the coils 32 and 33, the measuring circuit is inductively coupled with coil 3! of the oscillator. This output circuit may be adjusted to resonate with the ultra-high frequency oscillation generated by the vacuum tubes by means of an adjustable capacitance 36. The midpoint of the coil 34 is connected to ground through the ultra-high frequency choke coil 35. The purpose of the high frequency choke coil 35 is to provide a power frequency path toground and prevent the possibility of injury to the patient from the power voltages. The capacitance 35 is arranged as two equal series capacitances with the movable middle portion connected to ground. These ground connections are for the purpose of balancing the circuit to ground and in that way largely prevent the flow of longitudinal currents which if permitted to fiow would cause unequal currents to flow through output terminals 2 and it which are connected across the anti-resonant points of the output tuned circuit. To provide an indication of resonance when adjusting the capacitance 36 and of the magnitude of the ultra-high frequency output, the measuring circuit is provided with a thermocouple 3'? whose heater is connected across the coil 34 and whose meter is connected to a sensitive direct current meter 40 through ultra-high frequency choke coils 33 and 39. The meter 45 is shunted by a capacitance 4| to by-pass whatever ultra-high frequency current the coils 38 and 39 fail to suppress. The usual electrodes are connected to the output terminals 42, 33 and the patient or the part of the body to be treated is placed between these electrodes.

Obviously, some of the features of the invention may be modified. The oscillator may be useful in other structures, the output circuit may be coupled with other types of oscillators, etc.

What is claimed is:

1. In an apparatus for 'diathermic treatment, two vacuum tube oscillators each having a filament, a grid and a plate electrode, a filament and a plate current transformer, a source of alternating current connected with the primary windings of said transformers, connections joining the secondary winding of the filament transformer the filaments of said tubes to form a closed circuit, one point of said circuit being grounded, a secondary winding for the plate transformer grounded at a point intermediate its ends, a connection between the two grids includ- 75 two coils coupled ing an induction coil connected at its midpoint to one end of the plate transformer secondary, a condenser bridged across said one end of the plate transformer secondary and the grounded point of the secondary winding, a connection between the two plates including an inductance coil connected at its midpoint to the other end of the plate transformer secondary, an output circuit including a coil coupled with the last mentioned induction coil, an inductance in said output circuit, a variable capacitance bridged across said coil and inductance, and a measuring circuit bridged across said inductance.

2. In an apparatus for diathermic treatment, two vacuum tube oscillators each having a filament, a grid and a plate electrode, a filament and a plate current transformer, a source of alternating current connected with the primary windings of said transformers, connections from the secondary winding of the filament transformer to the filaments of said tubes including two choke coils one point of said connections being grounded, a voltmeter, a high frequency bypass around said voltmeter, a connection from said voltmeter across said filaments in parallel, a choke coil in each branch of the last mentioned connection presenting high impedance to current of a frequency within the range of the oscillators, a secondary winding for the plate transformer grounded at a point intermediate its ends, a connection between the two grids including an induction coil, a high frequency choke coil con nected at one end to the midpoint of said induction coil and at the other end to one end of the plate transformer secondary, a condenser bridged across said one end of the plate transformer secondary and the grounded point of the secondary winding, a connection between the two plates including an inductance coil, a high frequency choke coil connected at one end to the midpoint of the last mentioned inductance coil and at the other end to the other end of the plate transformer secondary; an output circuit including with the last mentioned induction coil and an uncoupled coil interconnecting the last mentioned two coils, a high frequency choke coil connected from ground to the midpoint of said uncoupled coil, a variable capacitance bridged across the output circuit and having grounded movable elements; and a measuring circuit bridged across said uncoupled coil and including a thermocouple, a direct current meter shunted by a condenser, and a high frequency choke coil in each limb of the measuring circuit.

3. A high frequency oscillator comprising two vacuum tubes each having a filament, a grid and a plate electrode, a filament and a plate current transformer, a source of alternating current connected with the primary windings of said transformers, connections from the secondary winding of the filament transformer to the filaments of said tubes including two choke coils one point of said connections being grounded, a voltmeter, a high frequency shunt around said voltmeter, a connection from said voltmeter across said filaments in parallel, a choke coil in each branch of the last mentioned connection presenting high impedance to current of a frequency within the range of the oscillators, a secondary winding for the plate transformer grounded at a point intermediate its ends, a connection between the two grids including an induction coil, a high frequency choke coil connected at one end to the midpoint of said induction coil and at the other end to one end of the plate transformer secondary, a condenser bridged across said one end of the plate transformer secondary and the grounded point of the secondary winding, a connection between the two plates including an inductance coil, and a high frequency choke coil connected at one end to the midpoint of the last mentioned inductance coil and at the other end to the other end of the plate transformer secondary.

4. In an apparatus for diathermic treatment two vacuum tubes each having a cathode, a grid and an anode, a high-frequency oscillatory circuit including said anodes, said anodes being connected in the circuit at such points that the oscillatory potentials on said anodes are in opposite phase, a source of low frequency alternating current, means including a transformer connected to said source and connections from the transformer secondary to the cathodes, grids and anodes of both tubes for applying simultaneously to the grid and anode of each tube bias potentials alternating with respect to the cathode potential at the frequency of said source of alternating current, the two grid bias potentials being in phase with each other but of opposite polarity with respect to the potentials of every point of the cathodes from the corresponding plate bias potentials, and all said bias potentials being substantially constant during a number of cycles of the oscillator circuit.

5. In an apparatus for diathermic treatment, a high-frequency oscillator having a resonant circuit including an inductance coil, a variably tunable output circuit symmetrical with respect toground comprising a variable condenser in series with an impedance, two portions of said impedance being magnetically coupled to said inductance coil and another uncoupled portion of said impedance being connected serially between said first two portions, and a current indicating device connected across only said other portion for indicating the current flowing in said output circuit.

6. In an apparatus for diathermic treatment, a high frequency oscillatory circuit for generating high frequency oscillations, including two vacuum tubes, each having a cathode, a grid and an anode, said tubes being connected in said circuit in push-pull relationship with respect to the high frequency oscillations to be generated, a source of low frequency alternating current, means for applying bias potentials which alternate above the highest and below the lowest cathode potential at the frequency of said alternating current from said source simultaneously to the grid and anode of each tube, the two grid bias potentials being in phase with each other but of opposite polarity with respect to the oathode potentials from the corresponding plate bias potentials, and all said bias potentials being substantially constant during a number of cycles of the high frequency oscillations, and means for heating said cathode from said source.

7. In an apparatus for diathermic treatment, two vacuum tubes, each having a filament, a plate and a grid electrode, an oscillating circuit including in series the grid to plate capacities of said tubes and two inductances, one of which is connected between the two grids and the other of which is connected between the two plates, a source of current, a connection from said source to said filaments, means for connecting said source with the plates and grids including a transformer and connections extending from the ends of the transformer secondary branchingly through said inductances to said plates and grids, a connection between an intermediate point of the transformer secondary and the filaments, an output circuit coupled with said oscillating circuit, and means for variably tuning said output circuit.

8. In an apparatus for diathermic treatment, two vacuum tubes, each having a filament, a plate and a grid electrode, an oscillating circuit including in series the grid to plate capacities of said tubes and two inductances, one of which is connected between the two grids and the other of which is connected between the two plates, a source of current, a connection from said source to said filaments, means for connecting said source with the plates and grids including a transformer and connections extending from the ends of the transformer secondary branchingly through said induotances to said plates and grids, a connection between an intermediate point of the transformer secondary and the filaments, an output circuit containing an inductance coupled with one of the inductances in the oscillating circuit, a variable capacitance in the output circuit, and a measuring circuit bridged across another inductance in the output circuit.

9. In combination, two-vacuum, tubes, each having a filament, a plate and a grid electrode, an oscillating circuit including the grids and plates of said tubes and two inductances of which one connects the two grids and the other connects the two plates, a source of current, a connection from said source to said filaments, means for connecting said source with the plates and grids including a transformer having a secondary, and circuits extending from the ends of said secondary dividedly through said inductances to the grids and plates, and a connection between an intermediate point of said secondary and the filaments.

10. In combination, two vacuum tubes, each having a filament, a plate and a grid electrode, a high frequency oscillating circuit including in series the grids and plates of said tubes and two inductances of which one connects the two grids and the other connects the two plates, a source of current, a connection from said source to said filaments, means including a transformer secondary of which each end is connected to one of said inductances for supplying low frequency alternating bias potentials from said source to the plates and grids, said bias potentials remaining substantially constant during a number of cycles of oscillation of said high frequency circuit, and a connection between an intermediate point of the transformer secondary and the filamerits.

FULLERTON D. WEBSTER. 

